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Failing Tests

Enable trace mode

It's a good idea to get as much information as possible about what's going on. We can enable trace mode during tests by running our tests with:

detox test --loglevel trace

Enable debugging of synchronization issues

See here.

Syntax Error: Unexpected Token

Issue: Running tests immediately throws the following error:

beforeEach(async () => {
SyntaxError: Unexpected token (
    at Object.exports.runInThisContext (vm.js:76:16)
    at Module._compile (module.js:545:28)
    at loader (/Users/builduser/buildAgent/work/34eee2d16ef6c34b/node_modules/babel-register/lib/node.js:144:5)
    at Object.require.extensions.(anonymous function) [as .js] (/Users/builduser/buildAgent/work/34eee2d16ef6c34b/node_modules/babel-register/lib/node.js:154:7)
    throw err;

Solution: This error means that your version of Node does not support async-await syntax. You should do the following:

  1. Update Node to a version 8.3.0 or higher.

Can't find my component even though I added testID to its props

Issue: Detox fails to match a component even though it has a testID. Detox will throw the following error:

Error: Cannot find UI Element.
Exception with Assertion: {
  "Assertion Criteria" : "assertWithMatcher: matcherForSufficientlyVisible(>=0.750000)",
  "Element Matcher" : "(((respondsToSelector(accessibilityIdentifier) && accessibilityID('Welcome')) && !kindOfClass('RCTScrollView')) || (kindOfClass('UIScrollView') && ((kindOfClass('UIView') || respondsToSelector(accessibilityContainer)) && ancestorThatMatches(((respondsToSelector(accessibilityIdentifier) && accessibilityID('Welcome')) && kindOfClass('RCTScrollView'))))))",
  "Recovery Suggestion" : "Check if element exists in the UI, modify assert criteria, or adjust the matcher"

Error Trace: [
    "Description" : "Interaction cannot continue because the desired element was not found.",
    "Domain" : "",
    "Code" : "0",
    "File Name" : "GREYElementInteraction.m",
    "Function Name" : "-[GREYElementInteraction matchedElementsWithTimeout:error:]",
    "Line" : "119"

Solution: React Native only supports the testID prop on the native built-in components. If you've created a custom composite component, you will have to support this prop yourself. You should probably propagate the testID prop to one of your rendered children (a built-in component):

export class MyCompositeComponent extends Component {
  render() {
    return (
      <TouchableOpacity testID={this.props.testID}>
          <Text>Something something</Text>

Now, adding testID to your composite component should work:

render() {
  return <MyCompositeComponent testID='MyUniqueId123' />;

Test tries to find my component before it's created

Issue: Due to a synchronization issue, the test tries to perform an expectation and fails because it runs the expectation too soon. Consider this example:

await element(by.text('Login')).tap();
await expect(element(by.text('Welcome'))).toBeVisible();

In the test above, after tapping the Login button, the app performs several complex asynchronous operations until the Welcome message is displayed post-login. These can include querying a server, waiting for a response and then running an animated transition to the Welcome screen. Detox attempts to simplify your test code by synchronizing automatically with these asynchronous operations. What happens if for some reason the automatic synchronization doesn't work? As a result, Detox will not wait correctly until the Welcome screen appears and instead will continue immediately to the next line and try to run the expectation. Since the screen is not there yet, the test will fail.

Solution: When you suspect that automatic synchronization didn't work, you have a fail-safe by synchronizing manually with waitFor. Using waitFor will poll until the expectation is met. This isn't a recommended approach so please use it as a workaround and open and issue to resolve the synchronization issue.

Full documentation about waitFor is available here. This is what the fixed test would look like:

await element(by.text('Login')).tap();
await waitFor(element(by.text('Welcome'))).toBeVisible().withTimeout(2000);

Can't synchronize the test with my app

If you suspect that the test is failing because Detox fails to synchronize the test steps with your app, take a look at this in-depth synchronization troubleshooting tutorial.

detox build or detox test are failing to run

Issue: Trying to run detox build or detox test throws the following error:

Error: Cannot determine which configuration to use. use --configuration to choose one of the following:
  at Detox.initConfiguration (/Users/rotemm/git/github/detox/detox/src/Detox.js:73:13)
  at Detox.init (/Users/rotemm/git/github/detox/detox/src/Detox.js:49:16)
  at process._tickCallback (internal/process/next_tick.js:103:7)

Solution: You have configured more than one configuration in your package.json and detox cannot understand which one of them you want to run. The error will print a list of available configurations, choose one by using --configuration option.

Run your commands with one of these configurations, for example:

  • detox build --configuration ios.sim.debug
  • detox test --configuration ios.sim.debug

Issue: In an attempt to run detox test the following error is thrown:

detox[4498] INFO:  [test.js] node_modules/.bin/mocha --opts e2e/mocha.opts --configuration ios.sim.release --grep :android: --invert

  error: unknown option `--configuration'

Solution: Upgrade to detox@^12.4.0 and mocha@^6.1.3. That weird error has been spotted in older versions of mocha (including 5.2.0) and fixed since 6.0.0. In fact, it conceals the genuine error:

Error: No test files found

If the error appeared after running a short command like detox test, please try out detox test e2e (in other words, append the path to your end-to-end tests folder) - and if that fixes the error, then you deal the bug in the question and upgrading detox and mocha should help.

Here's why you need to upgrade to detox@12.4.0. In 12.1.0 there was a premature deprecation of "specs" property in detox section of package.json. The deprecation was revoked in detox@12.4.0, and since then "specs" property acts as a fallback if a test folder has not been specified explicitly.

After you upgrade, you can configure the default path to your end-to-end tests folder in package.json (no deprecation warnings starting from 12.4.0), as shown below:

   "detox": {
-    "specs": "",  
+    "specs": "your-e2e-tests-folder",

Please mind that if your e2e tests are located at the default path (e2e), then you don't need to add "specs" property explicitly to package.json.

Debug view hierarchy

Issue: I added the testID prop but I still can't find the view by id in my tests.

Solution: You can investigate the app's native view hierarchy, this might shed some light on how the app's view hierarchy is laid out.

Do the following:

  1. Start a debuggable app (not a release build) in your simulator

  2. Open Xcode

  3. Attach Xcode to your app's process

  1. Press the Debug View Hierarchy button

  1. This will open the hierarchy viewer, and will show a breakdown of your app's native view hierarchy. Here you can browse through the views

  2. React Native testIDs are manifested as accessibility indentifiers in the native view hierarchy

Let's see an example. We will find the following view in the native hierarchy:

<TouchableOpacity onPress={this.onButtonPress.bind(this, 'ID Working')}>
  <Text testID='UniqueId345' style={{color: 'blue', marginBottom: 20}}>ID</Text>

This is the hierarchy viewer, pointing to the native view just mentioned:

Compare to a working setup

If you feel lost, try starting from a working example for sanity.

There are multiple working examples included in this repo, such as demo-react-native.

First, install, build and make sure the tests are indeed passing. If they are, try comparing this setup with what you have.

Take a look at past issues

Before opening a new issue, search the list of issues on GitHub. There's a good chance somebody faced the same problem you are.

How to open a new issue

Before opening a new issue, please follow the entire troubleshooting guide and go over past issues.

Include the following information in your issue to increase the chances of resolving it:

  1. Versions of all dependencies - iOS version you're working on, simulator model, React Native version, Detox version, etc

  2. The trace log of the test (see above)

  3. Source code of your test scenario

  4. If possible, try to extract a reproducable example of your issue in a git repo that you can share

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